In recent years, wideband high performance synthesizers have been widely employed in various applications, most of which are implemented with a multi-band VCO to cover a wide frequency range, as shown, for example, generally at 300 in FIG. 3. It is preferable to have a small gain for VCO to achieve better performance. Unfortunately, however, this gain must be able to cover the frequency deviations due to temperature change, and crystal wander, because it is undesirable to change the band control code (D<0:n>) once the synthesizer has been locked. This frequency deviation is generally at least several percentages around the center oscillation frequency. What's more, if the center frequency is very high, the issue is more severe. For instance, if the center frequency is 6 GHz, the frequency deviation is 20000 ppm, and the control voltage range is 1V, the corresponding VCO gain should be 240 MHz/V. This value is usually unacceptable in high performance synthesizer design. Thus, it is urgently desirable to find a technique to decouple this trade-off.